Remember that after Trump filed bankruptcy for the nth time, he couldn't get a loan from a U.S. bank. He went to Russian banks and Don Jr. even talked about going to Russian banks for money.
When Donnie couldn't do all the things Putin demanded after installing Trump in the WH, those banks/oligarchs/the Russian mob called in their loans. So Trump made a deal. He'd give Russia classified intel and Russia would cancel part or all his debt.
I don't know any of this for certain. What I do know is Trump is a traitor who would do anything for money.